Lotus’ high octane mix

Cars could run on biofuels more efficiently with a new research engine being developed by Lotus Engineering.

The sports car manufacturer is teaming up with Queen’s University Belfast and Jaguar Cars to develop a single cylinder engine prototype specially designed to run on sustainable bioethanol, synthetic methanol and petrol mixtures.

The engine, which is planned to be unveiled in January 2009, will use a variable-compression ratio system and a two-stroke operating cycle with direct fuel injection.

There are a small number of cars with flex-fuel engines on the market, including the Peugeot 307 1.6 BioFlex and Citroën C4 1.6 BioFlex. But the drawback is that currently they get fewer miles to the gallon running on biofuels. Lotus engineers hope the OMNIVORE engine will not require drivers to choose between efficiency and more sustainable fuel.

Engines designed specifically for alcohol-based fuels usually perform well, but designing an engine that can handle multiple fuels presents many challenges.

Typically, the best performing engines have high compression ratios, which makes them more prone to engine knocking — an erratic form of combustion that occurs when multiple flames spontaneously generate throughout the combustion chamber. The phenomenon is the result of excessive heat and pressure in the combustion chamber that causes the air/fuel mixture to autoignite.

The multiple flames will collide and create shockwaves that produce a sharp metallic pinging or ‘knocking’ noise in the engine. Prolonged knocking can cause extreme damage.

Petrol is unsuitable for engines with high-compression ratios, but alcohol-based fuels work well because they have a higher-octane level — which is a measure of resistance to knocking. The higher the octane number, the better the fuel is able to resist knocking.

Lotus engineers have taken this into account and is designing a flex-fuel engine with a variable compression ratio system that can be scaled back to a lower compression when running on regular petrol or a blend of petrol and bio alcohol.

The OMNIVORE programme complements the recently unveiled Lotus research on the complex combustion process involved in running on mixtures of alcohol fuels and petrol.

At this year’s Geneva Motor Show the company unveiled the Exige 270E Tri-fuel a 270bhp flex-fuel car capable of running on petrol, ethanol and methanol.

Mike Kimberley, chief executive of Lotus, said the company’s engineers are not only working on developing more efficient vehicles but also all aspects of future fuels and for alternative powertrains that will accommodate alcohol fuels as they enter the market.

‘Alcohols possess superior combustion characteristics to petrol which allows greater optimisation,’ he added. ‘Taking full advantage of the benefits of sustainable bio alcohols will ensure a greater percentage of vehicle miles will be travelled using renewable fuels.’

Kimberley said he was delighted with DEFRA’s investment that will help take forward research, development and the demonstration of the technology.

Siobhan Wagner

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